setpgid(2) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

SETPGID(2)              Linux Programmer's Manual             SETPGID(2)

NAME         top

       setpgid, getpgid, setpgrp, getpgrp - set/get process group

SYNOPSIS         top

       #include <unistd.h>

       int setpgid(pid_t pid, pid_t pgid);
       pid_t getpgid(pid_t pid);

       pid_t getpgrp(void);                 /* POSIX.1 version */
       pid_t getpgrp(pid_t pid);            /* BSD version */

       int setpgrp(void);                   /* System V version */
       int setpgrp(pid_t pid, pid_t pgid);  /* BSD version */

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       getpgid():
           _XOPEN_SOURCE >= 500
               || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

       setpgrp() (POSIX.1):
           _XOPEN_SOURCE >= 500
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc <= 2.19: */ _SVID_SOURCE

       setpgrp() (BSD), getpgrp() (BSD):
           [These are available only before glibc 2.19]
           _BSD_SOURCE &&
               ! (_POSIX_SOURCE || _POSIX_C_SOURCE || _XOPEN_SOURCE
                   || _GNU_SOURCE || _SVID_SOURCE)

DESCRIPTION         top

       All of these interfaces are available on Linux, and are used for
       getting and setting the process group ID (PGID) of a process.
       The preferred, POSIX.1-specified ways of doing this are:
       getpgrp(void), for retrieving the calling process's PGID; and
       setpgid(), for setting a process's PGID.

       setpgid() sets the PGID of the process specified by pid to pgid.
       If pid is zero, then the process ID of the calling process is
       used.  If pgid is zero, then the PGID of the process specified by
       pid is made the same as its process ID.  If setpgid() is used to
       move a process from one process group to another (as is done by
       some shells when creating pipelines), both process groups must be
       part of the same session (see setsid(2) and credentials(7)).  In
       this case, the pgid specifies an existing process group to be
       joined and the session ID of that group must match the session ID
       of the joining process.

       The POSIX.1 version of getpgrp(), which takes no arguments,
       returns the PGID of the calling process.

       getpgid() returns the PGID of the process specified by pid.  If
       pid is zero, the process ID of the calling process is used.
       (Retrieving the PGID of a process other than the caller is rarely
       necessary, and the POSIX.1 getpgrp() is preferred for that task.)

       The System V-style setpgrp(), which takes no arguments, is
       equivalent to setpgid(0, 0).

       The BSD-specific setpgrp() call, which takes arguments pid and
       pgid, is a wrapper function that calls

           setpgid(pid, pgid)

       Since glibc 2.19, the BSD-specific setpgrp() function is no
       longer exposed by <unistd.h>; calls should be replaced with the
       setpgid() call shown above.

       The BSD-specific getpgrp() call, which takes a single pid
       argument, is a wrapper function that calls

           getpgid(pid)

       Since glibc 2.19, the BSD-specific getpgrp() function is no
       longer exposed by <unistd.h>; calls should be replaced with calls
       to the POSIX.1 getpgrp() which takes no arguments (if the intent
       is to obtain the caller's PGID), or with the getpgid() call shown
       above.

RETURN VALUE         top

       On success, setpgid() and setpgrp() return zero.  On error, -1 is
       returned, and errno is set to indicate the error.

       The POSIX.1 getpgrp() always returns the PGID of the caller.

       getpgid(), and the BSD-specific getpgrp() return a process group
       on success.  On error, -1 is returned, and errno is set to
       indicate the error.

ERRORS         top

       EACCES An attempt was made to change the process group ID of one
              of the children of the calling process and the child had
              already performed an execve(2) (setpgid(), setpgrp()).

       EINVAL pgid is less than 0 (setpgid(), setpgrp()).

       EPERM  An attempt was made to move a process into a process group
              in a different session, or to change the process group ID
              of one of the children of the calling process and the
              child was in a different session, or to change the process
              group ID of a session leader (setpgid(), setpgrp()).

       ESRCH  For getpgid(): pid does not match any process.  For
              setpgid(): pid is not the calling process and not a child
              of the calling process.

CONFORMING TO         top

       setpgid() and the version of getpgrp() with no arguments conform
       to POSIX.1-2001.

       POSIX.1-2001 also specifies getpgid() and the version of
       setpgrp() that takes no arguments.  (POSIX.1-2008 marks this
       setpgrp() specification as obsolete.)

       The version of getpgrp() with one argument and the version of
       setpgrp() that takes two arguments derive from 4.2BSD, and are
       not specified by POSIX.1.

NOTES         top

       A child created via fork(2) inherits its parent's process group
       ID.  The PGID is preserved across an execve(2).

       Each process group is a member of a session and each process is a
       member of the session of which its process group is a member.
       (See credentials(7).)

       A session can have a controlling terminal.  At any time, one (and
       only one) of the process groups in the session can be the
       foreground process group for the terminal; the remaining process
       groups are in the background.  If a signal is generated from the
       terminal (e.g., typing the interrupt key to generate SIGINT),
       that signal is sent to the foreground process group.  (See
       termios(3) for a description of the characters that generate
       signals.)  Only the foreground process group may read(2) from the
       terminal; if a background process group tries to read(2) from the
       terminal, then the group is sent a SIGTTIN signal, which suspends
       it.  The tcgetpgrp(3) and tcsetpgrp(3) functions are used to
       get/set the foreground process group of the controlling terminal.

       The setpgid() and getpgrp() calls are used by programs such as
       bash(1) to create process groups in order to implement shell job
       control.

       If the termination of a process causes a process group to become
       orphaned, and if any member of the newly orphaned process group
       is stopped, then a SIGHUP signal followed by a SIGCONT signal
       will be sent to each process in the newly orphaned process group.
       An orphaned process group is one in which the parent of every
       member of process group is either itself also a member of the
       process group or is a member of a process group in a different
       session (see also credentials(7)).

SEE ALSO         top

       getuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3), termios(3),
       credentials(7)

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                          2021-03-22                     SETPGID(2)

Pages that refer to this page: gawk(1)strace(1)fork(2)getsid(2)setsid(2)syscalls(2)exit(3)killpg(3)posix_spawn(3)tcgetpgrp(3)credentials(7)pthreads(7)signal-safety(7)system_data_types(7)